Evidence of energy levels due to nitrogen dimers in silicon

Nitrogen-and-boron doped Czochralski Si samples are converted into n-type by annealing at 600 °C due to formation of Shallow Thermal Donors (STDs). The temperature dependence of the electron concentration, measured by Hall effect down to the liquid Helium temperature, is not however consistent with existence of only STDs and compensating boron acceptors; there is clearly an extra acceptor species with a level close to the conduction band, and of a concentration comparable to the total concentration of nitrogen. This acceptor centre is thus identified with the major nitrogen species, N2 and N2O. These two species can be distinguished by using samples from the seed-end and tail-end of a crystal: the level due to N2 is about Ec −27 meV, and that due to N2O about Ec −33 meV.